Brain Connectivity Varies Between Men and Women

Researchers at University of Pennsylvania have discovered fundamental differences between the neural wiring of the male and female brain. The human brain has four hemispheres—two in the cerebrum and two in the cerebellum. This is one of the largest studies to analyze the "connectomes" between—and within—each of the brain’s four hemispheres.

Major intra- and inter-connective differences were found in the left and right hemispheres of both the cerebrum and the cerebellum depending on gender. Past studies have shown sex differences in the brain, but the neural wiring connecting regions across the whole brain had never been studied in a large population until now.

The Penn Medicine study titled, "Sex Differences in the Structural Connectome of the Human Brain," was published December 2, 2013 in the Proceedings of National Academy of Sciences.

Ragini Verma, PhD, an associate professor in the department of Radiology at the Perelman School of Medicine at the University of Pennsylvania, and colleagues, found greater neural connectivity from front to back and within one hemisphere in males. This suggests that the male brain may be structured to facilitate greater connectivity between perception and coordinated action.

In females, the researchers found that the wiring was generally greater between the left and right hemispheres. This connectivity facilitates communication between the analytical and intuitive. "These maps show us a stark difference—and complementarity in the architecture of the human brain that helps provide a potential neural basis as to why men excel at certain tasks, and women at others," according to Verma.

For this study, Verma and colleagues investigated the gender-specific differences in brain connectivity during the course of development in 949 individuals (521 females and 428 males) aged 8 to 22 years using diffusion tensor imaging (DTI). DTI is water-based imaging technique that can trace and highlight the fiber pathways connecting the different regions of the brain, laying the foundation for a structural connectome or network of the whole brain.

Gender May Dictate Inter and Intra Brain Connectivity

Each individual's brain is an intricate and unique system of neural pathways that connect multiple networks within the cerebrum to several sub-networks in the cerebellum. The mysterious and powerful cerebellum is only 10% of brain volume but houses over 50% of your brain’s total neurons. Neuroscientists are still perplexed by the many functions of the cerebellum and why it has so many neurons.

My father—who was a neurosurgeon and neuroscientist—always said, "Whatever the cerebellum is doing, it's doing a lot of it." This study offers some interesting clues on the various roles of the cerebellum based on gender.

In this study, the researchers found that females displayed greater connectivity between the left and right hemispheres of the cerebrum. Males, on the other hand, displayed greater connectivity within each of the two hemispheres of the cerebrum.

On the flip side, the opposite occurred in the cerebellum where males displayed greater inter-hemispheric connectivity and females displayed greater intra-hemispheric connectivity.

The researchers believe these connections may give men an efficient system for coordinated action, where the cerebellum and cerebrum participate in bridging perceptual experiences in the back of the brain, and action, in the front of the brain. The female connections likely facilitate integration of the analytic and sequential processing modes of the left hemisphere with the spatial, intuitive information processing modes of the right side, according to the authors.

These findings were consistent with another Penn behavior study that demonstrated pronounced differences between the sexes. In that study females outperformed males on attention, word and face memory, and social cognition tests. Males performed better on spatial processing and sensorimotor speed. Those differences were most pronounced in the 12 to 14 age range.

Conclusion: Male and Female Brains Are Complementary and Varied

Next steps for the researchers will be to quantify how an individual's neural connections differ from the larger population to make each person unique. The researchers want to identify which neural connections are gender specific and which are the same in both men and women. Although this study makes some sweeping generalizations, it is interesting to note statistical patterns of connectivity that vary between the sexes.

Dr. Ruben Gur, a co-author of the study, concludes, "It's quite striking how complementary the brains of women and men really are. Detailed connectome maps of the brain will not only help us better understand the differences between how men and women think, but it will also give us more insight into the roots of neurological disorders, which are often sex related."

If you’d like to read more on this topic, please check out my Psychology Today blog posts:

For the moron geezer boomers, CBS Morning News' Norma whats-her-face and her evil twin-of-Oprah sidekick had a lesbian love moment over how "women use both sides of their brains, while men only use one side of theirs" -- basically the pop-feminist propaganda of 20-25 yrs ago.

Ragini Verma said "These maps show us a stark difference--and complementarity--in the architecture of the human brain that helps provide a potential neural basis as to why men excel at certain tasks, and women at others,”

Indeed, the difference in architecture is so stark that one would reasonably expect males and females to be totally different. But this is not what we find occurring: the difference between the genders is much smaller than the differences found within each gender.

My conclusion to the study: A stark difference in brain architecture has a surprisingly insignificant effect on brain function compared to the highly significant functional difference found between individuals with similar architecture.

I was amused by "men excel at certain tasks, and women at others," ... "Males performed better on spatial processing and sensorimotor speed." -- there are some damned good female navigators and pilots. My point being that excelling at certain tasks is, by definition, a rare ability that does not correlate with the brain maps in the study neither does it correlate with gender.

The study itself is fascinating, but its conclusions and the media hype are sensationalism: pop-neuroscience rather than science.

Increasing the size of a study does indeed increase its statistical significance, but does not necessarily increase its practical significance, and it does not add weight to induced conclusions (unless one is selling news stories).

Thank you for joining the discussion and for your insightful comment anonymous.

I also found this study very interesting but had some questions about the sweeping generalizations made by the researchers based on gender.

In writing this blog post, I tried to be as objective about the researcher's findings and conclusions as possible ... Experts seem to have a wide range of opinions on the link between gender and brain connectivity. I was hoping for comments and other opinions from readers like yourself. Thank you again for sharing your viewpoint and insightful conclusions on this study.

For me, the most promising aspect of the Penn research was summed up in the conclusion made by Dr. Ruben Gur who said these findings "will also give us more insight into the roots of neurological disorders, which are often sex related."

Another reader shared an article by 'neuroskeptic' that questioned the DTI method of imaging used in the study itself... This is all interesting food for thought and I really appreciate you taking the time to share your ideas about this study with myself and other readers.

Thanks very much for your reply, Christopher. I always enjoy reading your articles because I find them both highly informative and very well balanced (you have the rare ability to cut through the hype and present the essence).

I noticed (but regrettably failed to comment on) the important conclusion made by Dr. Ruben Gur: "[these findings] will also give us more insight into the roots of neurological disorders, which are often sex related." -- this would be a wonderful eventual outcome from the study.

The Neuroskeptic article was justified in questioning the validity of the study, not for the reasons given, but simply because it is the first study of its kind. The study will only gain credence when it has been independently verified.

Wow. This is awesome! Thank you again for advancing this discussion and sharing these insights. The dead salmon in the fMRI was brilliant. :-)

Also, thanks for shedding more light on the Neuroskeptics take on the new Penn study and DTI...You seem extremely knowledgeable on this topic and it's wonderful to have your feedback posted in these comments.

As I've mentioned before, my dad was a neuroscientist and neurosurgeon who became frustrated with the limitations of brain imaging technology in his research... Obviously, these technologies still have a long way to go. That said, I find all the new research and methods for studying connectomes really fascinating...

btw--I'm really glad you enjoy reading my blogs posts! Thank you for the kind words. I try very hard to keep my posts accessible and balanced while still pushing the envelope a bit. Like my dad, I am always looking for practical ways to apply the latest neuroscience to improving people's lives here and now.

Constructive comments like yours make a big difference in keeping the findings of these studies more balanced and on target. So again, I appreciate you taking the time to share your insights with myself and other readers. Have a great day! Christopher Bergland

PS--My sister is a pilot for FedEx and flies MD-11s around the globe. I couldn't agree with you more about the potential backlash of making sweeping generalizations about being a 'good navigator' based solely on gender and not an individual's unique brain architecture etc.